Cellular mobile stations, such as a mobile phones and personal digital assistants, have become increasingly common in recent years. In general, a cellular mobile station communicates over an air interface with a base station, which provides the mobile station with access to network resources, such as a communication channel to interact with other devices or with network servers.
In a typical cellular wireless communication system, multiple base stations are positioned throughout a market area, and each base station radiates to define wireless coverage areas such as cells and, in turn, cell sectors, in which mobile stations can operate. One or more base stations are then typically coupled or integrated with a base station controller, which manages air interface operation such as use of air interface channels and handoff of mobile stations between sectors. In turn, one or more base station controllers may be coupled with a switch (e.g., mobile switching center) or gateway (e.g., packet data serving node) that provides connectivity with a transport network such as the public switched telephone network (PSTN) or the Internet. With this arrangement, a mobile station may communicate via a base station, base station controller, and the switch or gateway, with entities on the transport network.
Air interface communication between the base station and a mobile station may operate in accordance with various air interface protocols, well known examples of which include CDMA (e.g., 1xRTT, 1xEV-DO), WiMAX (e.g., IEEE 802.16), iDEN, TDMA, AMPS, GSM, GPRS, UMTS, and EDGE, among others now known or later developed.
In general, each base station in a cellular wireless communication system broadcasts a pilot signal in each of its wireless coverage areas, to enable mobile stations to detect the presence of the wireless coverage areas and to facilitate handoff between the coverage areas. In practice, when a mobile station is served by a given coverage area, if the mobile station detects a sufficiently stronger pilot signal from another coverage area, the mobile station may initiate a handoff to the other coverage area. For instance, the mobile station may send a pilot strength management message over an air interface control channel, to notify its serving base station controller that the mobile station has detected a threshold stronger coverage area. With approval from the base station controller, the mobile station may then hand off to the new coverage area. Handoffs such as this can occur as a mobile station moves away from one base station and approaches another, and/or as the scope of wireless coverage areas change (e.g., the areas expand and contract) due to variations in network load or other factors.
An important feature of contemporary cellular wireless networks is an ability to determine the location of a mobile station. Such a feature was initially developed to assist emergency services in locating mobile stations. However, the availability of location information to support emergency services has given rise to the development of many other location-based service (LBS) applications as well. For example, given the location of a mobile station, a location based service provider (e.g., a cellular wireless service provider or a third party) can provide the mobile station's user with information related to that location, such as a weather or traffic report, a list of services or establishments (e.g., restaurants, parks, or theatres), and/or a map of the user's location with directions for travel between the user's location and another location. Many other examples are possible as well.
Several mechanisms exist to determine the location of a mobile station. A most rudimentary mechanism, for example, is to simply determine the location of the wireless coverage area that is currently serving the mobile station. In some systems, for instance, each base station may broadcast its geographic location coordinates. Thus, a served mobile station may receive the base station indication of location, and that location may be used as a generalized representation of the mobile station's location.
More advanced location determination mechanisms involve use of satellite positioning technology, such as the Global Positioning System (GPS). With such a system, to determine the location of a mobile station, the mobile station may measure round trip signal delays from nearby base stations and report the delay measurements to a mobile positioning center (MPC) in the network. The MPC may then use the reported delay measurements as a basis to estimate the mobile station's location. Given the location estimate, the MPC may then determine which satellites should be in the sky over the mobile station, and the MPC may direct the mobile station to tune to those satellites so as to receive satellite signal data. Once the mobile station receives the necessary satellite signal data, the mobile station may then report the data to the MPC, and the MPC may then use the satellite signal data as a basis to more accurately compute the mobile station's location.
In general, these location determination processes can be triggered by a request from a user of the mobile station or by a request from some other party. By way of example, a user of the mobile station may invoke an application on the mobile station to determine the mobile station's location or to determine information based on the mobile station's location. In response, the mobile station may then invoke a location determination process, to facilitate response to the user's request. The mobile station may then report or use the determined location itself and/or may provide the determined location to a location based service provider to facilitate a location based service. As another example, a location base service provider may request the mobile station's location, through interaction with the MPC or the mobile station, which may trigger a location determination process to facilitate providing the location based service provider with the mobile station's location. Other examples are possible as well.
Unfortunately, however, problems exist with these existing location determination processes. Use of base station location as a representation of mobile station location, for instance, while simple and inexpensive, is inherently inaccurate due to the scope of base station coverage areas. In particular, if a wireless coverage area spans a number of miles as is typical, representing the location of a mobile station by the location of its serving base station may have significant uncertainty. Use of satellite positioning, on the other hand, while far more accurate, suffers from a further drawback in terms of consumption of network resources. In particular, to facilitate satellite based location determination, the mobile station typically needs to communicate with the MPC via one or more air interface control or traffic channels, thus limiting the resources available for other use in the network. Consequently, an improvement is desired.